Terpenoids Derived Natural Products from Euphorbiaceae and Thymelaeaceae Families Velaydham Ramadoss,& Rafael Ortiz Alvarado, César R

REVISTA NATURALEZA Y TECNOLOGIA UNIVERSIDAD DE GUANAJUATO NO 9,ABRIL DEL 2016 ISSN:2007-672X

Terpenoids derived Natural products from Euphorbiaceae and Thymelaeaceae families Velaydham Ramadoss,& Rafael Ortiz Alvarado, César R. Solorio Alvarado,&* David Cruz Cruz,& and Eduardo Peña Cabrera&

& Universidad de Guanajuato, Campus Guanajuato. División de Ciencias Naturales y Exactas. Departamento de Química. Noria Alta S/N. Guanajuato, Guanajuato. C.P. 36050. Universidad Michoacana de San Nicolás de Hidalgo. Morelia, Michoacán. * [email protected]

CONTENTS: 1. Introduction (b) Phorbol, 2. Terpenoids isolated from Euphobia (c) Jatrophane, and Thymelaeace families. 3. Biological activities (d) Ingenol. 4. Synthesis of diterpenes derived natural products 5. Conclusions (a) Tigliane, 6. References

1. Introduction: Natural products have played an activities. Their great structural diversity, important role throughout the world in the resulting from various macrocyclic and treatment and prevention of human diseases. polycyclic skeletons including different Natural products serve as a vast source of aliphatic and aromatic acids.4 compounds with a broad range of chemical Diterpenes are considered to be important and functional diversity, as well as taxonomic markers because of their limited providing a rich source of new drugs and occurrence. These types of diterpenes are therapeutic agents.1-3 specific to the Thymelaeaceae and Diterpenes occurring in plants of the genus Euphorbiaceae families. Over 650 Euphorbia are the focus of natural product diterpenoids, incorporating more than 20 drug discovery because of the wide range of skeletal types, have been isolated from their therapeutically relevant biological Euphorbia plant.5

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Terpenoids isolated from Euphobia and phorbol esters, contains five hydroxyl Thymelaeace families. groups that possess different levels of reactivity towards a acylation. Most phorbol Diterpenes isolated from species belonging esters exist as the diesters, although a few to the Euphorbiaceae and Thymelaeaceae phorbol esters also exist in the form of families the tigliane diterpenoids are based triesters.7 on a 5/7/6/3- tetracyclic ring system 2.2. Esters of 12-Deoxyphorbol: consisting of a five-membered ring A, a seven-membered ring B, a six-membered A new parent alcohol, 12-deoxyphorbol, ring C, and a cyclopropane system D. The was obtained from a variety of different skeleton contains 20 carbons, consisting of plants including Excoecaria bicolor, five methyl, five methylene, and nine Euphorbia triangularis and Euphorbia methane groups, as well as one quaternary resinifera. 12-Deoxyphorbol can be readily carbon. Almost all of the reported tigliane esterified at the C-13 and C-20 positions, diterpenoids exist in the form of aglycons, and 12-deoxyphorbol esters exist and only three tigliane glycosides have been predominantly in one of two groups. The isolated, to date, from plant species first group consists of diesters with an belonging to the Euphorbiaceae and acetate moiety at C-20 and a long-chain Thymelaeaceae families.6 fatty acid at C-13, whereas the second group 2.1. Phorbol Esters consists of 13-monoesters with a free Plant species belonging to the hydroxy group at C-20. Although these Euphorbiaceae and Thymelaeaceae families compounds are more widely distributed than are known to produce “cryptic” phorbol phorbol esters, they are less stable.8-10 esters. Phorbol, the parent diterpene of

OH OR1 OR O OH 2 O HO H H

HO H HO H H O O HO HO O HO OH OH OH OH OH OH ingenol Jtrophane (+) - Phorbol Phorbol ethers structure Scheme 1. Terpenoids isolated from Euphobia and Thymelaeace families.

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2.3. Esters of 4,12-Dideoxyphorbol and ranging between three and eight. The most 4,12-Dideoxy(4α) phorbol heterogeneously esterified molecules are euphopeplin. El-Bassuony isolated two new 4,12-Dideoxyphorbols are oxygenated at C- jatrophane-type diterpenes, guyonianins C 13 and C-20, and have either 4β-H or 4α-H. and D, from the aerial parts of E. 4,12-Dideoxy(4α)phorbol and three of its guyoniana.13 Later, Hegazy et al. also esters have been isolated previously only investigated the chemical constituents of this from Excoecaria bicolor and Euphorbia species and isolated two new jatrophane guyoniana (Euphorbiaceae). To date, there diterpenes and one known jatrophane have been no reports in the literature diterpene from the aerial parts of the plant. focused on investigating the E. guyoniana is used traditionally in Algeria pharmacological potential of 4,12- for curing the venomous bites of scorpions dideoxyphorbol esters.11 and for removing warts.14 2.4. Esters of 12,20-Dideoxyphorbol To date, only two 12,20-dideoxyphorbols 2.7. Ingenanes. have been isolated from plants belonging to 12 the Euphorbiaceae family. O 2.5. Esters of 20-Deoxyphorbol Although very few 20-deoxyphorbols have been discovered to date, two 20- HO HO deoxyphorbols bearing a 5α-hydroxy moiety OH OH have been isolated from Synadenium Ingenane diterpenoids have a 5/7/7/3- grantii.13 tetracyclic ring system including a ketone 2.6. Jatrophanes. bridge between C-8 and C-10. A double O bond can be found in ring A between C-1 HO and C-2 and another between C-6 and C-7 in ring B. Moreover, a β-hydroxy group is linked to C-4, and rings A and B are HO H O transfused. In 2008, Lu et al. isolated new Jatrophane diterpenes occur exclusively in ingenane diterpenoids from the ethanol the Euphorbiaceae family, in general in the extract of E. esula.15 form of Polyesters. Natural jatrophane diterpenes are mainly polyacylated derivatives, the number of ester moieties

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3. Biological activities: 3.3 Anti-viral Activity Diesters of phorbol showed a potent anti- Compounds isolated from different HIV activity in MT4 cells with EC90 values Euphorbia and Thymelaeaceae species exert in the range of 0.00050− 1.52 μM, and many different activities, including anti- relatively low levels of cytotoxicity, with 18 inflammatory, MDR reversing, anticancer IC50 values in the range of 3.5−17.2 μM. activities.

3.1. Anticancer Activity 3.4 Multi Drug Resistance Reversing Generally, diterpenes exhibit tumor- Activity promoting activity, research published in the The most common tumors are resistant to last 20 years has also shown that some available drugs because of inhibition of P- derivatives show significant anticancer glycoprotein which represents a promising activity. For example, the 12-deoxyphorbol approach for overcoming the multiple drug derivatives showed antileukemic activity resistance. Diterpenens investigated for with ED50 values in the range of 0.4−3.4 MDR reversing activity, Compounds μg/mL in a P-388 lymphocytic leukemia withvarious skeletal types e.g., jatrophanes, system in vitro. Jatrophane diterpenes lathyranes, and “euphoractine-type” showed possess tumor cell growth inhibitory a significant MDR-reversal effects.19 activities on MCF7 (breast epithelial adenocarcinoma) cells.16 4. Synthesis of Diterpens: Diterpenes from Euphorbia and 3.2 Anti-inflammatory Activity Thymelaeaceae familes which exhibit a Pepluanone, a diterpene component of variety of interesting biological activities. Euphorbia peplus, possesses a high anti- The complex structure and striking inflammatory effect in vivo. They biological properties of diterpenoids have investigated the anti-inflammatory activity prompted chemists to devise a series of of six compounds with pepluane and synthetic strategies and methodologies for paraliane skeletons. The results showed that the constructing of their complexes all compounds have NO2− production structural frameworks. inhibitory activity in LPS-stimulated J774 macrophages by iNOS.17

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Intramolecular Diels−Alder Approach to first compound to be prepared synthetically synthesis Tigliane skeleton: possessing the complete tigliane skeleton Wender et al.20 published the first total and stereochemistry. However, it was synthesis of the tigliane skeleton in 1987, devoid of oxygenation at C-12 and C-13 and using an intramolecular Diels−Alder did not possess the A-ring functionalities cycloaddition and an intramolecular aldol required for conformational rigidity or the condensation as key steps in their synthesis attachment of lipophilic groups. (Scheme 1). The resulting phorboid was the

CH OBn 1) Ph =CH /toluene, 105 ¡C O 2 3 2 O 145 ¡C/Xylene 2) (COOH)2, SiO2/CH2Cl2 O O MeO 3) CH2=C(OTBS)OEt, MeO OMe MeO ZnCl2/CH2Cl2

BnO 4) HF/CH3CN

H Br Br 1) PhHgCBr3/benzene, 80 ¡C H H 2) TMSCN, ZnI2/CH2Cl2 H EtO2C EtO2C(H2C)2 O O O NC TMSO BnO BnO H Br 1) DIBAH/toluene, -78-0 ¡C Br 1) DIBAH/toluene, -78-0 ¡C 2) Me2CucnLi2/ether, -20 ¡C; MeI H H 3) o-NO2PhSeCN, Bu3P/Pyridine 2) (COCl)2, Me2SO/CH2Cl2, -60 ¡C, Et3N CHO O 4) H2O2/THF

3) Bn2NH2CF3CO2/benzene TMSO 5) Bz2O, DMAP, Et3N, /CH2Cl2 BnO 6) Znl2/TMSCN

7) Bu4NI/HMPA H 1) t-BuLi/THF, -78 ¡C H 2) TMS-Im/CH Cl H 2 2 H 3) SeO2, (CH3)3COOH/CH2Cl2, 0 ¡C H O H OH OH BzO TMSO TMSO I TMSO

1) SOCl2/Et2O, 0 ¡C H

2) KOAc-TMEDA, AgOAc/CH3CN H 3) TBAF/THF H OH HO HO OH 1 Scheme 2. Synthesis of Tigliane skeleton and its stereochemistry

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Total synthesis of synthesis (+)-Phorbol: system of phorbol, followed by an Oxyallyl [4+3] Cycloaddition Approach adaptation of Wender’s efficient method for the construction of the A ring. This synthesis 21 In 2001, Cha et al reported the formal of the phorbol intermediate required more synthesis of (+)-phorbol using Wender’s steps and was less efficient than the method advanced intermediate. As shown in Scheme developed by Wender, although this work 2, their synthetic plan was built upon a [4+3] effectively demonstrated the applicability of oxyallyl cycloaddition and subsequent this strategy to the construction of tiglianes intramolecular Heck reaction for the and daphnanes. stereocontrolled construction of the BC-ring OTBS OTBS OAc O HF; AC2O O Cl Cl Et3N, CF3CH2OH O O O Cl Zn, MeOH. O

OTBS OTBS OAc

OAc 1) TBSCl OBOM 2) K CO Candida rugosa 2 3 NaOMe 3) BOMCl MeOH O O O O

Ph N Ph OH Li OTBS 1) LiCl, TMSCl, NIS 2) allyltributylin OBOM OH H 1) PhCCLi, LiBr H 1) Swern oxidation 2) TMSOTf O O O O O Ph 2) Ph3P TMSO OTBS OTBS O Ph I O X 5 mol% Pd(OAc) 1) MeMgBr, CuBrDMS 2 HCO K H H 2 2) LiBH4 H + n-Bu4N Br- O O 3) Swern Oxid Ph Ph O Ph 4) Ph P CHI TMSO TMSO 3 OTBS OTBS TMSO OTBS

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H Ti(O-i-Pr) O H 4 H CrO3/DMP i-PrMgBr O O O OTMS OTMS Ph OTBS Ph OTBS Ph OTMS OTBS

O OH OH H H L-Selectride Wender's methods O HO H O OTMS OH Ph OTBS OH

(+) - Phorbol

Scheme: 3. Formal synthesis of (+) - Phorbol

Synthesis of a Jatrophane diterpene:

In 1989, the total synthesis of (±)- by Katsumura et al.22 The synthetic route jolkinolides A, B, and E from 10- contained approximately 20 reaction steps. (methoxycarbonyl)-β-ionone was performed

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Scheme. 4: (A) Synthetic route toward the production of a jatrophane diterpene structural fragment. Reagents and conditions: (a) (i) LiAlH4, THF, rt (90%); (ii) Me2C(OMe)2, PPTS, CH2Cl2, rt

(85%);(iii) O3, CH2Cl2, MeOH, −78 °C, PPh3 (90%); (b) (i) CBr4, PPh3,CH2Cl2, −78 °C; (ii) MeLi, THF,

−78 °C; MeI, −78 °C to rt (78%); (c) Cp2Zr(H)Cl, THF, 40 °C, 1.5 h, then 12, CH2Cl2, (80%). (B) Synthetic route toward the production of a jatrophane diterpene structural fragment.

Reagents and conditions: (a) (PhSe)2, NaBH4, MeOH, 0 °C, 30 min, to rt (91%); (b) LiNiPr2, iPrCN,

Et2O, 0 °C to rt (93%); (c) iBu2AlH, toluene, −78 °C, 1 h (81%); (d) BrMgCH=CH2, THF, −78 °C, 45 min (76%); (e) NAH, (PMB)Cl, n-Bu4NI, THF, DMSO (90%). (C) Total synthesis of a jatrophane diterpene. Reagents and conditions: (a) 9-BBN, THF, 40 °C, 24 h,

+ II (100 mol%), (dppf)PdCl2 (7 mol %), Ph3As (20 mol %), Cs2CO3 (270 mol %),THF, DMF, H2O

(14/2/1), 80 °C, 8 h (86%); (b) (i) H2O2, NaHCO3, H2O, THF, rt (68%); (ii) La(NO3)3·6H2O, MeCN, 50

°C, (54%); (iii) IBX, CH2Cl2, DMSO (1/1), rt (81%); (c) (i) H2C=C(Me)Br, tBuLi, THF, −78 °C, 15 min

(91%); (ii) DDQ, CH2Cl2, aq pH 7 buffer, rt, 2.5 h; (iii) IBX, CH2Cl2, DMSO (1/1), rt, 6 h (75%); (d) (i)

III (10 mol %), toluene (c = 1.3 × 10−3 mol/L), 110 °C, 2 h; (ii) HF·Py, THF, 0 °C, 3 h; (e) (i) PPh3,

DIAC, p-BrC6H4COOH, THF, 0 °C (87%); (ii) MeOH, K2CO3, rt, 5 h (91%).

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Total synthesis of Ingenol: Ingenol has also been of great interest not of ingenol was performed by Winkler with only because of its unusual structure the use of an intramolecular de Mayo containing an “inside−outside” bridged BC reaction. Other successful synthetic ring, but also because of a broad spectrum of approaches (Winkler, Wood, and pharmacological activities. The synthesis of Tanino/Kuwajima) and promising partial the highly strained ingenane framework syntheses have since been reported and required special approaches and strategically reviewed. distinct methods.23 The first total synthesis

a-b c MeO2C

O O O

O d e O

O O

O O f g O O H H O O OPMB OPMB

O h O i j

O H HO H OPMB OPMB

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O O O k l

O O O O O OPMB HO OPMB HO O OPMB

O O m n o

O O O O HO SO2Ph OH SO2Ph

HO HO OH OH

ingenol 32 steps, 0.2% overall yield Scheme: 5. Wood’s total synthesis of ingenol.

Reagents and conditions : (a) (i) (HOCH2)2, p-TsOH, C6H6, Δ, 96%, dr = 43:23:18:16; (ii)

LiAlH4, Et2O; (iii) HCl, acetone, H2O, 95% (two steps); (b) (i) Ac2O, pyridine, DMAP, 96%; (ii)

DBU, C6H6, Δ , 80%; (c) cyclopentadiene, BF3·OEt2, PhCH3, −78 °C, 59%; (d) Grubbs-I, ethylene, CH2Cl2, 98%; (e) (i) OsO4, NMO, THF−H2O (4:1); (ii) NaIO4, MeOH−THF (4:1); (iii)

(HOCH2)2, p-TsOH, C6H6, Δ, 73% (three steps); (f) ClCH2C( CH2)CH2O(PMB), KH, THF, Δ,

98%; (g) RCM, P, hCH3, Δ, 76%; (h) (i) HCl, THF−H2O, Δ; (ii) NaBH4, EtOH−THF, 0 °C, 77%

(two steps); (iii) I2, PPh3 imidazole, THF, 0 °C; (iv) KOtBu, THF−DMSO, 94% (two steps); t (i) (i) SeO2, BuOOH, CH2Cl2−H2O−HOAc, 0 °C, rt, 68% based on recovered starting material

(brsm); (ii) Dess−Martin periodinane (DMP), CH2Cl2, −40 → +10 °C, 74%; (iii) RhCl3, EtOH, t t 115 °C, 74%; (j) KO Bu, O2, P(OMe)3, THF, BuOH (4:1), −40 °C, 94%; (k) VO(acac)2, t BuOOH, C6H6, 10 °C to rt, 73%; (l) (i) (TMS)OTf, Et3N, CH2Cl2, −10 to −5 °C, 72%; (ii)

NaBH4, MeOH; (iii) 2,2-DMP, PPTS, CH2Cl2, Δ,86% (two steps); (m) (i) DDQ, CH2Cl2, 90%;

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(ii) MsCl, Et3N, CH2Cl2, −78 °C, 96%; (iii) PhSH, Li2CO3, DMF, 55 °C, 76%; (iv)

(NH4)6Mo7O24,H2O2, EtOH, 97%; (n) DBU, C6H6, Δ, 47%; (o) (i) Na−Hg, Na2HPO4, MeOH,

−20 → −10 °C, 76%; (ii) HCl, THF−H2O, 92%; (iii) SeO2/SiO2,THF, 80 °C, 85% brsm.

Total synthesis of Ingenol by Phil Baran et al :24 Finally the shorthest synthesis of ingenol by Professor Phil S. Baran is following described.

Me Cl Me Me a. NCS Me c.LiNap, MeI Me Me Me O Me b. O3, thiourea O then LiHMDS, H 48 % over 2 steps C OH C O d. Me Me 44 % one-pot

Me Me Me Me e. TBSOTf; d. MgBr Me Me TMSOTf TMSO HO H H 81%, 10:1 d.r 71% C OH C OTBS Me Me

Me Me f. [RhCl(CO)2]2 Me Me TMSO TMSO CO, xylenes O Me g. MeMgBr Me Me H 0.005M H HO OTBS 80% OTBS 72% Me Me cyclase-phase end point Me Me Me Me Me O Me O Me BF .Et O Me SeO2, 3 2 H H then AC2O OTBS ACO -78 ¡C to 40 ¡C, then OTBS 59% O O O MeOH/Et3N O Me O O Me

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Me Me Me Me Me O Me O Me BF .Et O Me SeO2, 3 2 H H then AC2O OTBS -78 ¡C to 40 ¡C, then OTBS ACO O O 59% MeOH/Et N O Me 3 O O O Me

Me Me Me Me Me O Me O Me HF Me c. Martin sulfurane H H then NaOH 90% OH HOHO ACO O 81% HO Me O O Me

Me Me SeO2 Me O Me HCO H 2 H OH HOHO HO OH

5. CONCLUSIONS Diterpenes from Euphorbiaceae and the assessment of anti-proliferative, ant- Thymelaeaceae families are considered to be cancer, MDR inhibitory, anti-inflammatory, important taxonomic markers because of and antimicrobial activities. Researchers are their limited occurrence and structural working towards the elucidation and diversity. In the past few years, more than biological activity of different diterpenoids, 200 novel diterpenes have been isolated and it is envisaged that some of these from different Euphorbia and diterpenoid derivatives will be developed Thymelaeaceae species.25 Recent into useful materials with a variety of pharmacological experiments encompassed different applications in the future.25

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6. REFERENCES

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